The present invention relates generally to the methods and system for using an improved reaction frame to isolate reaction forces created during manufacturing and further includes using the improved reaction frame in a photolithographic system for precision manufacturing of semiconductor devices.
Overlaying or superimposing many layers of circuit patterns on a wafer typically produces the semiconductor device. The circuit pattern is first formed in a reticle and transferred onto a surface layer of the wafer through photolithography. This requires precise alignment of the wafer relative to the reticle during the photolithography process.
A typical photolithography apparatus includes an illumination source, a reticle stage assembly retaining a reticle, a lens assembly and a wafer stage assembly (i.e., the object stage) retaining a semiconductor wafer. The reticle stage assembly and the wafer stage assembly are supported above ground with an apparatus frame. Typically, the wafer stage assembly includes one or more motors to precisely position the wafer and the reticle stage assembly.
The typical wafer stage assembly includes a stage base, a first stage and a second stage. The stages move relative to the stage base to position the wafer. The first stage is used for relatively large movements of the wafer along an X-axis. The second stage is used for relatively large movements of the wafer along a Y-axis. Existing wafer stage assemblies typically include a fixed guide with an air bearing that inhibits the first stage from moving along the Y-axis and rotating about a Z-axis relative to the stage base.
Motors moving the stage along the X-axis and Y-axis during processing create reaction forces. These reaction forces can be a problem in a photolithographic system used for processing wafers and generating chips because the size and the images transferred onto the wafer from the reticle are extremely small. Vibration introduced by these reaction forces misaligns the wafer and images superimposed on the wafer to create the chip. Consequently, it is critical to the manufacturing of high density, semiconductor wafers to control these reaction forces and keep the wafer or part aligned.
As the circuit density of integrated circuits increases and feature size decreases, alignment errors caused by these reaction forces must be further reduced or eliminated. Conventional reaction frames used to process wafers deliver a majority of the reaction forces to ground. Each portion of the reaction frame is typically attached to ground using a ground rod or some other means to transfer the vibration and reaction force directly to ground.
Unfortunately, some chip manufacturers cannot secure each portion of the reaction frame directly to ground. For example, a manufacturer may only have a single wall available to secure a portion of a reaction frame in a photolithographic system. If portions of the reaction frame are not secured or grounded, reaction forces may continue to introduce vibration and ultimately misalign the wafers during the manufacturing process. It would be advantageous to develop a reaction frame design that works in a variety of different manufacturing situations and addresses this problem. For example, the reaction frame should work to reduce vibration from reaction forces in a photolithography system whether secured to ground by a single wall or by multiple walls.
In precision manufacturing, a stage assembly holds a wafer or object in place while being processed using photolithography and other precision manufacturing processes. Drive mechanisms moving the wafer or object in one or more degrees of freedom within the stage assembly often create undesirable reaction forces. Left alone, these reaction forces may cause the stage assembly to move, vibrate or lose alignment. To combat these reaction forces, a reaction frame diverts the reaction forces from the stage assembly and reduces vibration and potential misalignment. An improved reaction frame is provided having multiple reaction frame portions that work together to alleviate the effects of the reaction forces. The reaction frame portions are coupled together using an interconnect rod that efficiently transfers reaction forces to ground without causing the reaction frame portions to dynamically couple, rotate or translate in position. The improved reaction frame and interconnect can be used in a variety of precision manufacturing situations including photolithographic processing of wafers
One aspect of the invention includes a reaction frame having a first reaction frame portion and a second reaction frame portion that receives reaction forces from a stage. The first reaction frame portion is coupled to ground in a first direction by a ground rod aligned along the longitudinal side of the first reaction frame portion. A second reaction frame portion of the reaction frame not coupled directly to ground in the first direction but is coupled to an interconnect rod passing parallel to the plane defined by the first reaction frame portion and second reaction frame portion. The interconnect rod has a first end and a second end with a damper therebetween, wherein the first end is coupled to the first reaction frame portion and the second end is coupled to the second reaction frame portion and reaction forces in the first direction received by the second reaction frame portion are transferred to ground through the interconnect rod and the first reaction frame portion.
Another aspect of the invention includes a reaction frame having a first reaction frame portion and a second reaction frame portion that receives reaction forces from a stage. Typically, the reaction forces are generated by a drive mechanism moving a stage. The first reaction frame portion of the reaction frame is coupled to ground in a first direction by a first ground rod aligned along the longitudinal side of the first reaction frame. A second reaction frame portion of the reaction frame not coupled directly to ground in the first direction is connected to ground using an interconnect rod having a first end and a second end. The first reaction frame portion is alligned with the ground rod, wherein the first end is coupled to the first reaction frame portion and the second end is coupled to the second reaction frame portion and reaction forces in the first direction received by the second reaction frame portion are transferred to ground through the combination of the interconnect rod and the first reaction frame portion.
Implementations of the invention may include one or more of the following advantages or features. Multiple reaction frame portions making up the reaction frame both absorb reaction forces and transfer the reaction forces to ground through a ground rod. The interconnect rod and damper allows the reaction frame to be separated into reaction frame portions to accommodate different stage assembly configurations. Because the reaction frame is modular, manufacturers can use this reaction frame style under many different situations. With the interconnect rod, the overall reaction frame can be installed with fewer ground rods as the interconnect rod transfers the reaction forces from several reaction frame portions to a ground rod. The damper on the interconnect rod helps prevent multiple reaction frame portions to dynamically coupling causing the reaction frames portions to either rotate or translate causing misalignment. In some cases, the damper may not be necessary if the stage assembly has room to run the interconnect rod between the reaction frame portions aligned along the line of force.